The present invention relates to a method and a device for manufacturing a nonwoven material by hydroentangling a fibre web.
Hydroentanglement or spunlacing is a technique which was introduced in the 1970-ies, see e.g. the patent No. CA 841 938. The technology involves forming either a dry-laid or wet-laid fibre web, whereafter the fibres are entangled, i.e. intertwined, by means of very fine water jets at a high pressure. Several rows of water jets are directed towards the fibre web which is supported by a moving wire. The entangled fibre web is then dried. The fibres which are used in the material can be constituted of synthetic or regenerated staple fibres, e.g. polyester, polyamide, polypropylene, rayon and the like, of pulp fibres, or mixtures of pulp fibres and staple fibres. Spunlaced materials can be manufactured with a high quality at a reasonable cost and exhibit a high absorption capacity. For instance, they are utilised as wiping materials for domestic or industrial use, as disposable materials within medical care and hygiene, etc.
During the entanglement, the fibre web is supported by either a wire or a perforated, cylindrical metal drum. An example of a hydroentanglement unit of the latter type is disclosed e.g. in EP-A-0 223 614. This type of hydroentanglement unit makes great demands upon the sealing of the suction boxes. However, supporting members in the form of wires of the type utilised in connection with paper production is the most frequently occurring type.
One disadvantage with such wires is that the fibre web, as a result of the strong action it is subjected to during the hydroentanglement, penetrates into and is caught between the wire threads, wherein it can be difficult to separate the final product from the wire in some cases. Furthermore, a woven wire results in limitations when choosing the structure and pattern of the final product which can be created in connection with the entanglement.
An object of the present invention is to provide a method and a device for manufacturing a nonwoven material by hydroentangling a fibre web, wherein the problem with removing the final product from the supporting member (wire) has been eliminated or at least reduced. According to one embodiment of the invention, this has been achieved by means of the fibre web being supported by a moulded screen of a thermoplastic material during the hydroentanglement.
In addition to the simplified removal of the final product from the supporting member, a moulded plastic screen also provides increased possibilities to create the desired aperture patterns and structures in a simple way in the nonwoven material which is manufactured.
Preferably, the moulded plastic screen is reinforced with reinforcement wires. The surface which supports the fibre web can be smooth or structured.
Another embodiment of the invention further relates to the use of a moulded, close-meshed screen of a thermoplastic material for supporting a fibre web during a hydroentanglement process. Today, such moulded plastic screens are utilised as a base material for manufacturing press felts for paper machines, wherein a fibrous material is laminated to the screen. However, according to this embodiment of the invention, only the base material in the form of the moulded plastic screen is utilised as a supporting material during the hydroentanglement.